Development of Small Molecules with a Noncanonical Binding Mode to HIV‑1 Trans Activation Response (TAR) RNA

Small molecules that bind to RNA potently and specifically are relatively rare. The study of molecules that bind to the HIV-1 transactivation response (TAR) hairpin, a cis-acting HIV genomic element, has long been an important model system for the chemistry of targeting RNA. Here we report the synthesis, biochemical, and structural evaluation of a series of molecules that bind to HIV-1 TAR RNA. A promising analogue, <b>15</b>, retained the TAR binding affinity of the initial hit and displaced a Tat-derived peptide with an IC₅₀ of 40 μM. NMR characterization of a soluble analogue, <b>2</b>, revealed a noncanonical binding mode for this class of compounds. Finally, evaluation of <b>2</b> and <b>15</b> by selective 2′-hydroxyl acylation analyzed by primer extension (SHAPE) indicates specificity in binding to TAR within the context of an in vitro-synthesized 365-nt HIV-1 5′-untranslated region (UTR). Thus, these compounds exhibit a novel and specific mode of interaction with TAR, providing important suggestions for RNA ligand design